434 Prof. H. Karsten on the Vegetable Cell. 
When the above-mentioned solvents for a cell-membrane 
engaged in chemical metamorphosis for the purpose of lignifica- 
tion are allowed to act upon a septum in process of thickening 
(fig. 40 a), and a stronger contraction is then induced in one of 
the two adjoining and adherent daughter cells by the agency of 
exosmotic fluids, the central and unthickened portion of the 
septum is torn through, whilst the peripheral walls of the two 
adherent sister cells remain connected, as indeed was observed 
although differently interpreted by Mohl (Vermischte Schriften, 
mi. '5, 9); 
The chemical and physical actions of the above-mentioned 
commonly employed reagents upon the substance of plants has, 
however, been by no means sufficiently studied to enable us, 
from the changes which they produce upon vegetable tissues, to 
arrive at any certain conclusions as to the structure of the latter. 
And our knowledge of the mode of action of these reagents 
upon the membranes of assimilant cells is especially imperfect, 
because it is different in each new stage of development of the 
cell, which is in a constant process of change. 
The intimate knowledge of the anatomical changes which 
take place in the cell in the course of development must there- 
fore precede, or at least go hand in hand with, that investigation, 
the results of which consequently, as yet, are of subordinate 
value in the appreciation of anatomical conditions. 
The mutual adherence of the constituent cell-membranes of 
the septum (p. 283), which stands so much in the way of a 
correct recognition of its true nature, appears to be still more 
inexplicable, under certain circumstances, in fully developed 
cells. In such cells the still delicate daughter cells are com- 
monly separated with great facility from the parent cell by the 
action of diosmotic fluids. But if a specimen of Conferva glo- 
merata be allowed to lie for some time in a dilute aqueous solu- 
tion of tannin or of ammonia, and an aqueous solution of iodine 
be then brought in contact with it, not only are the membranes - 
of the secondary cells loosened from those of the primary, but 
these last also are partially separated from the mother cell, and 
the enveloping membrane from the included joint-cells even to 
the very extremity (fig. 41). All the thickened membranes 
moreover show very clearly the thickening layers, which are — 
either imperceptible or very imperfectly recognizable in the 
living plant: this is the case especially after their penetration 
by a solution of gum arabic. The delicate membranes of the 
secondary cells are not, however, detached at both extremities, 
as in normal states, from the primary cell, but maintain their 
position as exhibited in fig. 47; and as they become contracted 
by exosmosis, they drag the primary membrane, which lies 
